private void prepareSubSystem() {
h = center.busy(SubSystemType.cpu);
if (h == null) {
Set<SubSystemType> types = new HashSet<SubSystemType>();
types.add(SubSystemType.cpu);
h = new Hierarchy(JSTORM_HIERARCHY_NAME, types,JSTORM_CPU_HIERARCHY_DIR);
}
rootCgroup = new CgroupCommon(root_dir, h, h.getRootCgroups());
}